【作者】 谭波；

【导师】 杨万勤； 吴福忠；

【作者基本信息】 四川农业大学 ， 生态学， 2010， 硕士

【摘要】 土壤动物群落的结构和功能在生态系统的物质循环和能量转换过程中具有十分重要且不可替代的作用和地位,因而全球范围内不同生态系统的土壤动物群落结构和功能等受到普遍的关注。季节性冻融是全球中高纬度和高海拔地区普遍存在的气候变化过程。现在的关键科学问题是：受季节性雪被和冻融循环影响明显的生态系统过程具有4个明显的关键时期(生长季节、土壤冻结初期、冻结期和融冻期),这4个关键时期的土壤动物群落是否发生显著变化?如何变化?生长季节与非生长季节的土壤动物群落结构和功能有何联系?但迄今缺乏深入系统的研究,这限制了人们对季节性冻土区土壤生态过程的理解。川西亚高山／高山森林地处青藏高原东缘和长江上游地区,是我国第二大林区(西南林区)的主体,在水源涵养、生物多样性保育、全球碳循环、指示全球气候变化、调节区域气候等方面具有十分重要且不可替代的作用和地位。作为中纬度高海拔地区最具代表性的森林生态系统,土壤冻结时间长达5-6个月,气候垂直分异明显,是研究全球变暖情景下冬季土壤生态学过程的理想科研场所。但迄今为止,季节性冻融对该区土壤动物群落结构和功能影响的研究尚未见报道,更缺乏从4个关键时期来研究亚高山森林生态系统过程的研究报道。因此,本研究以川西亚高山和高山地区分布面积最大和范围最广的原始冷杉林(Abies faxoniana)、针阔混交林(A. faxoniana, Betula albosinensis)和次生冷杉林为研究对象,采用干、湿漏斗法和手拣法研究了一个季节性冻融期间和生长季节(2008-11-1～2009-10-31)的土壤动物群落特征,这对于深入了解亚高山／高山森林冬季土壤生态学过程及其与生长季节生态过程的相互联系具有十分重要的意义。初步研究结论如下：3个森林群落的土壤温度在监测期间表现出显著的动态变化特征,土壤平均温度均以8月最高,1月最低。2008年11月～2009年4月为各森林群落的季节性冻融期,土壤12月上旬完全冻结,次年4月下旬完全解冻。原始林、混交林、次生林的土壤季节性冻融的起始时间分别为11月8日、11月9日、11月23日,冻结持续时间分别为157天、127天、120天,完全解冻时间分别为4月13日、3月15日、3月22日,冻融循环次数分别为20次、18次、11次。研究森林群落中共检出土壤动物159038只,原始林61313只,混交林55897只,次生林41828只,隶属7门16纲30目。可检出的土壤动物平均个体数量和类群数量以生长季节最高,冻结期最低。虽然各森林土壤在季节性冻融期间仍存在相当数量和类群的土壤动物,但土壤冻结和冻融循环显著影响了可检测的土壤动物个体和类群数量,平均个体数量最大比生长季节少3379只,类群数量最大比生长季节少18个。所选森林群落的土壤动物群落以鞘翅目(Coleoptera)、双翅目(Dipter)、蜱螨目(Acarina)、线虫纲(Nematoda)、弹尾目(Collembola)为优势类群,土壤冻结和冻融循环显著影响了土壤动物群落结构,蜘蛛目(Araneae)、带马陆目(Polydesmida)、异蛩目(Spirostreptida)、膜翅目(Hymenoptera)对冻融作用响应敏感。各群落有机土壤层的土壤动物个体密度和类群数量显著高于矿质土壤层,以生长季节最高,但混交林个体密度除外。原始林和次生林有机土壤层的大型土壤动物个体密度以8月5日最高,混交林以3月25日最高,而类群数量均以12月15日最低。原始林和混交林有机土壤层的中小型土壤动物个体密度以11月3日最高,次生林以10月20日最高,而原始林和混交林有机土壤层类群数量以12月15日最低,次生林以11月19日最低。土壤冻结和冻融循环显著影响了有机土壤层和矿质土壤层的土壤动物个体密度和类群数量,表现为随季节性冻结动态而先降低后增加的变化趋势,这种趋势在受冻融作用更为强烈、持续时间更长的原始林有机土壤层更显著,平均密度最大比生长季节降低了201±18只,平均类群最大比生长季节降低了14个,而有机土壤层的中小型动物个体密度同样表现出相似的变化,平均密度最大比生长季节降低了169±19(103)只,但类群数量不明显。原始林、混交林、次生林群落优势类群的大型土壤动物优势类群比例均以生长季节最低,混交林和次生林的中小型土壤动物优势类群比例变化以冻结期最低,原始林以生长季节最低。土壤冻结和冻融循环显著影响了优势类群蜱螨目和弹尾目个体密度及其比值(A／C),以原始林最显著,最大分别降低了286±26(102)只、134±22(102)只、0.94±0.21,特别是初冻期和融冻期。3个森林群落的Shannon-Wiener指数H’、Pielou均匀性指数J和Simpson优势度指数C同样受土壤冻结和冻融循环影响显著。大型土壤动物的指数H’和J总体表现为以生长季节最高,冻结期最低,指数C表现为融冻期最高,生长季节最低。中小型土壤动物的各指数变化不明显。与土壤动物群落相似,各森林群落土壤的可溶性有机碳、可溶性氮、微生物生物量碳、微生物生物量氮含量受土壤冻结和冻融循环显著影响也表现出明显的动态变化。同时以受冻融作用更为强烈、持续时间更长的原始林有机土壤层更显著,特别是初冻期和融冻期。相关分析表明,土壤动物群落密度与可溶性有机碳含量存在一定的负相关关系,与微生物生物量碳含量存在正相关关系。综合分析表明,川西亚高山／高山典型森林群落具有明显的季节性冻结和冻融交替特征。森林土壤即使在气候寒冷的冬季仍存在相当数量和类群的土壤动物。温度变化导致的土壤冻结和冻融循环对土壤动物群落施加强烈作用,显著影响了动物群落的结构和功能以及相关土壤生化特性,这在有机土壤层表现的更为明显。这些结果不仅证明了土壤动物群落对环境变化的敏感性,而且也表明了土壤的冻融时间、频度和强度对土壤动物群落结构施加了强烈影响,同时暗示着冻融作用驱动的土壤动物群落变化特征可能对深入认识冬季土壤生态过程及其与生长季节生态学过程的相互作用与相互关系具有重要意义。更多还原

【Abstract】 Many focuses have been paid on the structure and function of soil fauna community all over the world, since the important role in material cycling and energy transferation in ecosystem. Seasonal freeze-thaw cycle is the significant climate change processes in the regions with relative higher altitude and latitude. However, there are four obvious periods (the growing period, early frozen period, continuously frozen period and the thawing period) in the ecological processes as affected by seasonal snow-pack and freeze-thaw cycles in these areas. The currently crucial scientific questions are:whether or how does the soil fauna community change among the periods, what are the relationships between growing period and non-growing period? These unresolved questions limit our understanding of soil ecological processes in the areas with seasonal soil frozen.The alpine/subalpine forest of Western Sichuan is the representative forest in southwest China, which is located in the upper reaches of Yangtze River and transitional area between the Qinghai-tibet plateau and Sichuan basin, and plays important roles in conserving water and biodiversity, balancing global carbon cycling, and regulating regional climate. As one of most representative forest ecosystems in middle latitude region with relative high altitude, the alpine/subalpine forest is an optimal ideal site to study soil ecological processes in wintertime since its vertical distribution characteristic of climate, and obviously seasonal freezing of soil with a length of 5-6 monthes. So far, researches on the structure and fuction of soil fauna community in the alpine/subalpine forests of western Sichuan as affected by seasonal freeze-thaw have not been well documented, far less to ecological processes of the four key periods in this region. A field experiment was therefore conducted to investigate the composition, abundance, and diversity of soil fauna by Hand, Baermann and Tullgren methods in primary fir (Abies faxoniana) forest (PF), fir and birch (Betula albosinensis) mixed forest (MF) and secondary fir forest (SF), which were three representative and widely distributed forests in the subalpine and alpine forest region in western Sichuan, during the seasonal freeze-thaw period and next growing period from November 2008 to October 2009. The results are helpful to deeply understand the effect of seasonal freezing-thawing events on the process of the subalpine and alpine forest ecosystem and its relationship between the ecological processes in winter and summer.There were obvious seasonal dynamic characters of soil temperature in the three sampling forests, and the maximum and minimum average soil temperature were respectively recorded in August and January. Seasonal freeze-thaw period began in November 2008 and ended in April 2009. Meanwhile, soil had frozen in the early December 2008, and thawed in the latter April 2009. Seasonal freeze-thaw period respectively started on November 8, November 9 and November 23 in the PF, MF and SF, which respectively ended on April 13, March 15, and March 22. Furthermore, a total of 157,127, and 122 days length of continuously frozen period were respectively recorded in the PF, MF and SF. Correspondly, a total of 20 cycles,18 cycles, and 11 cycles of freeze-thaw cycle had also been respectively recorded in the PF, MF and SF.By preliminary identification,159038 individuals were detected, which belonged to 7 phyla,156 classes and 30 orders in the three sampling forests.61313,55897 and 41828 individuals were detected in the PF, MF and SF, respectively. The highest and lowest detectable individuals and groups of soil fauna were both respectively observed in the growing period and continuously frozen period. Although there were still comparable individuals and groups of soil fauna during seasonal freeze-thaw period, frozen and repeated freezing-thawing cycle of soil imposed significant influence on the structure and function of detectable soil fauna communities. In comparison with the growing period, the maximum average individuals and groups of soil fauna had respectively decreased 3379 individuals and 18 groups.The dominant groups were consisted of Coleoptera, Dipter, Acarina, Nematoda, and Collembola in the three sampling forests, meanwhile, frozen and repeated freezing-thawing cycle of soil imposed significant influence on the structure and function of soil fauna, and groups of Araneae, Polydesmida, Spirostreptida, and Hymenoptera were sensitive to freezing-thawing events.In comparison with the mineral soil layer, the soil organic layer had higher density and groups of soil fauna, and the highest density and groups of soil fauna were observed in the growing period, but except density of the MF. The highest density of macrofauna, which belonged to organic soil layer, were observed on 5 August in the PF and SF, and on 25 March in the MF, but the lowest groups of that were observed on 15 December in all sampling forests. Similarly, the highest densities of mesofauna and microfauna, which belonged to organic soil layer, were observed on 3 November in the PF and MF, and on 20 October in the SF, but the lowest groups of that were observed on 15 December in the PF and MF, and on 19 November in the SF. Frozen and repeated freezing-thawing cycle of soil imposed distinct influence on density and groups of soil fauna, and following dynamics of seasonal freezing-thawing, density and groups of soil fauna exhibited a decreased then increased trend, and this trend in soil organic layer was more significant in the PF, owing to higher intense and more frequent freeze-thaw cycles in soil organic layer of the PF. In comparison with the growing period, the maximum average density and groups of macrofauna had respectively decreased 201±18 individuals and 14 groups, correspongdly, the maximum average density of mesofauna and microfauna had decreased 169±19 (103) individualsThe lowest proportion of dominant groups of Marcofauna was in growing period in the three sampling forests, and the lowest proportion of dominant groups of Mesofauna and Microfauna was in frozen period of the MF and SF, and in growing season of the PF. Frozen and repeated freezing-thawing cycle of soil imposed dramatically influence on the density of Acarina and Collembola, and the value of Acarina to Collembola (A/C), this phenomenon was more significant in the PF. In comparison with others, the maximum average density of Acarina and Collembola respectively had decreased 286±26 (102) individuals、134±22 (102) individuals. the maximum value of Acarina to Collembola had decreased 0.94±0.21, especially in early frozen period and thawing periods.Furthermore, following freezing-thawing event, diversity indices of Shannon-Wiener (H’),Pielou (J) and Simpson (C) also obviously significant changed. The highest macrofauna indices of H’ and J was in growing season, and the lowest in frozen period, but the highest macrofauna index of C was in soil thawing period, and the lowest in growing season. Meanwhile, diversity indices of mesofauna and microfauna were no significant changed.Similarly, the dissolve organic carbon, dissolve nitrogen, microbial biomass carbon, and microbial biomass nitrogen obviously changed during this study in the three sampling forests too. Frozen and repeated freezing-thawing cycle of soil imposed dramatically influence on nutrient sequestration and mineralization and microbial structure, and this trend in soil organic layer was more significant in the PF, owing to higher intense and more frequent freeze-thaw cycles in soil organic layer of the PF, especially during early frozen and thawing period. Pearson’s correlation shown that density of soil fauna communities had certain degree negative correlation with dissolve organic carbon, and had positive correlation with microbial biomass carbon.In conclusion, the results indicated that there were obvious freeze-thaw cycles during seasonal freeze-thaw period in the subalpine and alpine forest of western Sichuan. These freeze-thaw cycles showed significant effects on the structure and function of soil fauna communities, especially which in soil organic soil layer. Moreover, the results not only revealed that soil fauna communities were sensitive to environmental change, but also indicated that the length, intensity and frequence of freeze-thaw cycles had significant effects on the structure and diversity of soil fauna community. Therefore, the changs in soil fauna community driven by freeze-thaw cycles could be contributed to understand the wintertime ecological processes, and the interaction in freeze-thaw season and growing period.更多还原